Many electronic systems require or benefit from power autonomy (i.e., the capability of operating from sources of power readily available in their environment instead of being connected to a power grid or batteries with a finite lifetime). This property is particularly desirable for portable electronic devices and electronic devices operating in remote locations (e.g., wilderness, deep sea, outer space) or otherwise inaccessible locations (e.g., inside a human body). Such electronic devices need some way to convert energy from its original form (e.g. optical, mechanical, thermal) into electrical energy.
The most common and mature technology enabling moderately-sized electronic devices to achieve power autonomy is photovoltaic conversion using, for example, solar cells. Although this technology works very well where sufficient light is available, it is not applicable in dimly-lit places or in locations that are inherently shielded from light, such as medical implants, inside building structures, deep sea, and underground. An alternative power conversion technology involves extracting energy from mechanical sources.
Electromechanical conversion currently is used to produce most of the power that is distributed on the regular power grid. Miniature electromechanical converters, on the other hand, have been developed to take advantage of a variety of mechanical power sources, such as ambient vibrations, human walking motion, wind, and water flow.
The invention features electromagnetic power converters that are operable to convert mechanical power into electrical power based on the variations in capacitance between electrodes that are moved relative to each other in response to mechanical energy.
In one aspect, the invention features an electromechanical power converter for delivering electric power to a primary load. The electromechanical power converter includes first and second electrodes, an electret, and a power extraction circuit. The first and second electrodes form a variable capacitor with a capacitance that varies over an operative capacitance range as a result of relative electrode movement in response to mechanical energy. The electret is disposed between the first and second electrodes. The power extraction circuit is coupled between the first and second electrodes and is operable to conduct charge between the electrodes through the primary load during a discharge phase and to set the electrodes to an inter-electrode reset voltage during a reset phase.
Other features and advantages of the invention will become apparent from the following description, including the drawings and the claims.